Descriptions

An oscillating plasma glow discharge detector for gas
chromatography is used to obtain fingerprint information
about an analyte by combining both the average cell
current and oscillation frequency signals. Five homologs
each of the n-alkanes, 1-alkenes, 1-alkynes, 2-ketones and
aldehydes are studied. Although triplicate determinations
had some scatter due to noise, they showed clustering that
allows several of these compounds to be distinguished from
the others by using a two-dimensional plot of the ratios
of frequency peak area to current peak area and frequency
peak height to current peak height.
Fingerprint identification information is improved by
changing the cell pressure, applied voltage and electrode
spacing. Changes in the discharge operating conditions
produce changes in the analyte peak responses. The
relative magnitudes of the analyte current and frequency
peak responses also change with respect to each other
under different discharge conditions. Unique fingerprints
or patterns of responses are created for each analyte by
changing the discharge operating conditions. The detector
responses toward 10 organic compounds, representing seven
different functional groups, are recorded under 56
different combinations of discharge conditions. The
ratios of the frequency to current peak responses (heights
and areas) for three of the 56 sets of conditions
investigated provide enough information to distinguish
between nine compounds. Principal component analysis and
hierarchical cluster analysis, multivariate exploratory
techniques, are used to observe natural clustering in the
data.